Fluorine containing layer on light metals



Eatented June 13, 3939 UNITED STATS FLUO RINE CONTAINING LAYER ON LIGHTMETALS Julius Still, Leverkusen-I. G. Wei-k, Germany, as-

signor, by mesne assignments, to Magnesium Development Corporation, acorporation of Delaware No Drawing. Application July 23, 1936, SerialNo. 92,251. In Germany July 27, 1935 3 Claims.

This invention relates to the manufacture of fluorine containing layerson light metals or.

10 In accordance with the present invention fluorine containing layersare prepared on light metals or alloys thereof, such as magnesium, thealloy thereof known under the trade-mark "Elektron", byelectrolysisusing as an electrolyte 15 a poly-acid fluoride having the compositionYF.::(HF) wherein a: is at least 2 and YF stands for a member of thegroup consisting of the alkali metal fluorides, ammonium fluoride, amidofluorides and amino fluorides. Besides the alkali 20 metal poly-acidfluorides and ammonium polyacid fluorides, there may be used thepoly-acid fluorides of amides or amines, such as of urea, acetamide,aniline, methylamine, ethylamine, diphenylamine, diethylamine,tetramethyl-ammo- 25 nium hydroxide and the like. Mixtures of the abovementioned poly-acid fluorides may be employed as well as mixtures of thesame with neutral fluorides or bifluorides, The poly-acid fluorides usedin accordance with the present-invention are characterized by having acomparatively low melting point, so that the process can be performed atlow temperatures and with slight consumption of energy, due to whichfact the process can also be applied to such metals or 35 alloys with acomparatively low melting point.

As suitable poly-acid fluorides there may be mentioned by way of examplethe potassium poly-. acid fluorides of the composition 'KF.2HF to KLMHF,the melting points of the said poly-acid 40 fluorides being between 60and '10v C.; furthermore, ammonium poly-acid fluorides of thecomposition NH4F.2HF to '-NH4F.5HF. melting between about 20 and 30 0.;further a mixture of poly-acid fluorides of the composition 45msnr+nmnnr in various proportions, for example in the ratio 1:1; or amixture of 80% of NH4F.2HF and 20% of NHJHF, the latter mixture meltingat 20 C.

Example 1.A magnesium sheet is placed into a melt of NH4F.2HFand used asthe anode. At 55 40-50 C. an electric current which is regulated bymeans of a regulating resistance to 1 ampere per square decimeter ispassed through for about minutes. Thereby the tension rises from about50 to about 135 volts. In this manner a fluorine containing layer isproduced on the magnesium sheet.

Example 2.In the same manner a fluorine containing layer is'produced ona plate of Elek- 5 tron" metal. The Elektron plate is used as the anode.As the electrolyte the salt of ZEEEHF is used and a current of ampereper square decimeter is passed through for about minutes at 80-90" C.The final tension is about 10 56 volts. 7

Example 3.'In an analogous manner a fluorine containing layer isproduced on a magnesium plate while working with a,mixture ofKF.2.5HF+NH4F.HF in the proportion 1:1 and passing through a current ofl ampere per square decimeter for 10 minutes at 100 C. The tensionduring the process rises to 58-62 volts.

,1. A process of forming a protective fluorine containing layer onarticles made of a metal of the group consisting of magnesium andmagnesium base alloys, which comprises subjecting a fused electrolyte,comprising at least one polyacid fluoride having the compositionYF.:r(HZF),

wherein a: is at least 2 and not more than 5 and YF stands for a memberof the group consisting of the alkali metal fluorides, ammoniumfluorides, amide fluorides and amino fluorides, to electrolysis whileemploying such metal article as the anode.

2. A process of forminga protective fluorine containing layer onarticles made of a metal of the group consisting of magnesium andmagnesium base alloys, which comprises subjecting a fused electrolyte,comprising at least one polyacid fluoride having the compositionYF.a:(HF), wherein a: is at least 2 and not more than 5 and YF standsfor a member of the group consisting of the alkali metal fluorides,ammonium fluorides, amido fluorides and amino fluorides, andat least onefluoride of the group consisting of' neutral fluorides and bifluorides,to electrolysis while employing such metal article as the anode. -3. Aprocess of forming a protective fluorine containing layer on articlesmade of a metal of the group consisting of magnesium and magnesium basealloys, which comprises subjecting a fused electrolyte having a meltingpoint not exceeding about 100 C. and substantially consisting of atleast onepoly-acid fluoride having the composition YF.a:(I-IF),.whereina: is at least 2 and not more than 5 and Y5 stands for a member of thegroup consisting of the alkali metal fluorides, ammonium fluorides,amido 5 fluorides and amino fluorides, to electrolysis while employingsuch metal article as the anode. JULIUS sou.

